The present invention relates to a microwave circuit for a parametric upper sideband down converter terminated at the image frequency by a real conductance and which has a parallel circuit at its input, an intermediate frequency (IF) circuit at its output, and a reactance diode coupling these circuits together.
The theoretical principles of operation and circuit variants for a parametric upper sideband down converter with real image frequency termination conductance and its interconnection with a prior art intermediate frequency amplifier are described in U.S. Pat. No. 3,991,373. The parametric upper sideband down converter discussed there is distinguished by conversion gain and, with the use of the real portion of the antenna impedance as the image frequency termination conductance, by an adaptivity with respect to the antenna temperature which, with low circuit and diode losses, permits the establishment of a quadrupole having a constant additional noise factor F.sub.z independent of the antenna temperature.